Many liquids that are stored in sealed containers, such as alcoholic beverages, fruit juices and dairy products (e.g. milk), rapidly deteriorate upon exposure to oxygen after the sealed containers are opened.
The introduction of “bag in a box wine” (wherein the wine is contained in a collapsible plastic bag held in a cardboard box and dispensed through a valve at the bottom of the container, closed with a plastic cap) addressed both the problem of oxygen intrusion and the problem of adequate closure after initial opening. But such a container structure has limitations in its practical use since the valve prevents a user from enjoying pouring the wine from the collapsible plastic bag into a second container, such as a goblet. Instead, the wine must be dispensed from the plastic bag in an upright position. The same problem applies to any other liquid contained in such kind of container.
On the other hand, today's supermarkets and shops sell beverages such as carbonated drinks in increasingly large volumes. The containers of these beverages are usually plastic bottles, and generally hold up to around 3 liters of liquid, although there is no reason why larger containers cannot be used. However, a problem with carbonated drinks, especially those stored in large containers, is that once the containers have been opened and a quantity of the beverage is consumed, the quality of the beverage, i.e. the degree of carbonation, causing the effervescence or “fizzyness,” and hence the taste, of the beverage remaining in the container, diminishes over a relatively short period of time. This is because consuming the beverage increases the space in the container for gases, and the increase of the space changes the gas/liquid pressure equilibrium between the beverage and the space. As a result, the carbon dioxide in the beverage escapes quickly into the increased space and the carbon dioxide concentration in the beverage decreases. As the beverage keeps being consumed, there is eventually only a negligible amount of carbon dioxide remaining in the beverage and the beverage remaining in the container has lost its desired taste and/or become undrinkable.